drm/msm: update mode2 entry sequence for sde rsc

Update mode2 entry sequence for sde rsc and change
bwi_threshold with timer slot_0 configuration. This
change also disables the double buffer configuration
before enabling vsync source for video mode display.

Change-Id: Ie85e748035d5c7e1093b002cba22e7cec980cb42
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>